For many patients with leukemia or disseminated solid tumors who have relapsed after standard therapy, very intensive chemo/radiotherapy followed by a marrow transplant offers the only realistic chance of long-term disease-free survival. Transplantation of the patient's own (autologous) marrow is used with increasing frequency in patients who are not candidates for allogeneic marrow transplants because of their age or because they lack histocompatible marrow donors. However, the full potential of autologous marrow transplantation cannot be realized unless we find ways to rid autologous grafts of occult clonogenic tumor cells. This proposal is molded around the hypothesis that photosensitization mediated by lipophilic merocyanine dyes such as MC 540 can be used to selectively kill residual tumor cells in autologous bone marrow grafts. Although MC 540-mediated photosensitization reduces the concentration of experimental leukemia cells greater than 100,000-fold without excessive damage to the pluripotent stem cell compartment, it may not be equally effective against some spontaneous tumors or not be sufficient for the purging of marrows with very high levels of neoplastic cells. We therefore want to determine if using MC 540 in combination with another purging agent (e.g. antibody, drug, hyperthermia) can augment its antineoplastic effect without increasing stem cells toxicity. A second set of experiments aims at identifying the cellular and molecular mechanisms that regulate the binding of MC 540 to cells and mediate the inactivation of cells by MC 540 and light. We will also complete a phase I and initiate a phase II clinical trial of MC 540-mediated photosensitization for the purging of autologous marrow grafts. In the context of this trial we will study the effects of dye- mediated photosensitization on hematopoietic stem cells and accessory cells in the graft, and its effects on engraftment and the recovery of immune function. The proposal work will generate new insights into the interactions of MC 540 and its photoproducts with nuclear DNA and plasma membrane lipids and proteins, the role of lipid peroxidation and protein crosslinking in MC 540-mediated cytotoxicity, and the clinical usefulness of merocyanine dyes. (Methods: Clonal assays of normal and neoplastic cells, marrow transplantation, dye-mediated photosensitization, hyperthermia, flow cytometry, computer simulation, manipulation and analysis of membrane lipids and proteins, UV/VIS- and fluorescence spectroscopy, somatic cell genetics.)